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Announcing OpenSprinkler Bee (OSBee) Arduino Shield v1.0

May 29th, 2014 by ray

Update: check out our new standalone OpenSprinkler Bee (OSBee) 2.0 with built-in WiFi and OLED display.

Two months ago, I wrote a blog post about the preview of OpenSprinkler Bee, which is an open-source arduino-based controller for battery-operated sprinkler valves. While that’s still in the development stage, today I am glad to announce that an Arduino shield version of OpenSprinkler Bee is completed and immediately available for purchase at the Rayshobby Shop.

Update: check out our new standalone OpenSprinkler Bee (OSBee) 2.0 with built-in WiFi and OLED display.

So what is this Arduino shield version, and how is this different from other OpenSprinkler prodcuts that we carry? Well, an Arduino shield is a circuit board that you plug into an existing Arduino — it does not have a microcontroller chip itself, but contains additional circuitry that extends the basic functionality of an Arduino. So to use the shield, you will need to provide an existing Arduino board.

How is the OpenSprinkler Bee (OSBee) different from the other OpenSprinkler products? The main difference is that OSBee is designed to work with battery-operated sprinkler valves. These valves internally use a latching solenoid, which only draws power when you open or close the valve, and does not draw power if it remains in the same state. So it’s very efficient and suitable for battery-operated controllers. The other OpenSprinkler products, such as OpenSprinkler 2.1s, DIY 2.1u, OSPi 1.4, OSBo 1.0, are all designed for 24V AC sprinkler valves, which operate on 24V AC and require a power adapter / transformer.

While OSBee shield itself does not have built-in wireless modules, you can stack it with other Arduino shields, such as RF, WiFi, Ethernet shields, to provide web connectivity. The OSBee Arduino library has one example of using the Arduino Ethernet shield with OSBee shield to create a web interface for sprinkler control.

Is there any easy way to tell latching solenoid valves from 24V AC valves? Yes. Latching solenoid valves usually come with a special plug, and the two wires are usually colored differently because the solenoid has polarity. 24V AC valves usually come with just two wires colored in the same way (because AC voltage has no polarity). Here are some examples of latching solenoid valves. Note the special plugs and/or different wire colors.

For valves that come with stripped wires, simply attach them to the screw terminal blocks on OSBee shield. For valves with special plugs, you can cut and strip two pieces of wire (20 to 24 AWG): insert one end of the wire to the plug, and the other end to the screw terminal block.

How to open or close the latching solenoid valve? Electrically, latching solenoid valves have quite low coil resistance (a few ohms). To open the valve, you apply a momentary positive voltage on the coil. The specific voltage depends on the valve specification, but it typically varies between 9V to 22V. To close the valve, just reverse the voltage polarity. The important thing to keep in mind is that the voltage is applied as a pulse — usually 25 to 100 milliseconds. Because the coil resistance is so low, the instantaneous current is very high, up to a few amps. So you can’t apply the voltage continuously (or it will smoke the coil or the power supply!) In addition, it’s better to first build up the voltage into a capacitor, and then dump the charge to the valve from the capaictor.

How to generate such a high voltage from Arduino’s 5V or 3.3V pin? It’s by using a neat circuitry called ‘boost converter‘. The Wikipedia has plenty of information about how it works, but the basic principle is to use a MOSFET switch, an inductor, a diode, and a PWM signal to build up the charge into a capacitor. This way you can generate a high voltage from a low-voltage source such as AA batteries.

How to apply a voltage in both polarities? This is by using another neat circuitry called ‘H-Bridge‘. The H-Bridge is made of four MOSFET switches. By closing the pair of switches in each diagonal direction, you can apply voltage in either positive or negative polarity. Because you also need a state where no voltage is applied on the solenoid, that’s three states in total and hence two microcontroller pins are required to produce three states. Wait, why not directly use two microcontroller pins to apply the voltage? Well, microcontroller pins can neither handle high voltage nor provide high current, so you need MOSFETs to help switch high voltage and high current using only logic signals from the microcontroller.

With all the technical concepts explained, here is the diagram of the various components on the OSBee Sheild:

The shield can switch 4 independent valves / zones. The boosting voltage is software adjustable — anywhere from 9V to 24V. An Arduino library with three demo programs are provided in the OSBee Github repository. For details, please refer to:

OSBee Shield v1.0 User Manual

OSBee Shield v1.0 is now available for purchase at the Rayshobby Shop. Thanks!

Posted in Arduino, Product News, Sprinkler Projects | 31 Comments »

At Bay Area Maker Faire 2014

May 17th, 2014 by ray

We are at the Bay Area Maker Faire at San Mateo Event Center. This year we got assigned to Station 5 (HomeGrown Village), which is a bit surprising because the past two years we’ve always been at Station 2 with the Arduino and Raspberry Pi gadgets. But this is probably an interesting change as we will be neighbors to other makers working on smart watering and home grown food. If you are at the faire, make sure to come by Station 5 and take a look at our gadgets. See you there!

Posted in Maker Faire, Sprinkler Projects | No Comments »

SquareWear 2.0 is now available at SeeedStudio.com

May 1st, 2014 by ray

This is a quick announcement that SquareWear 2.0 is now available for purchase at SeeedStudio.com.

This is great news for customers living outside of the US, because SeeedStudio offers excellent and low-cost international shipping options.

Posted in Arduino, Wearable | No Comments »

The Story of OpenSprinkler: an Open-Source Web-Based Sprinkler Controller

Apr 30th, 2014 by ray

Last week I wrote a short story on OpenSprinkler for the Make Magazine blog. It’s about how learning Arduino inspired me to invent the OpenSprinkler. Check out the blog post at the link below:

The Story of OpenSprinkler: an Open-Source Web-Based Sprinkler Controller

Thanks to everyone who helped and contributed to this project!

This year we will be having a booth at the Bay Area Maker Faire again. If you are going there too, make sure to drop by our booth and check out OpenSprinkler, SquareWear, AASaver, and the upcoming goodies. Thanks!

Posted in Maker Faire, Sprinkler Projects | No Comments »

Reverse Engineer Wireless Temperature / Humidity / Rain Sensors — Part 3

Apr 19th, 2014 by ray

Continuing from Part 1 and Part 2, this is the third and last post about how I reverse engineered a few off-the-shelf wireless temperature, humidity, and rain sensors, and used an Arduino to listen to and decode the sensor data. Update: RPi is also supported now! Check the provided programs at the end of this post.

Wireless Rain Sensor

Raw Waveform. There are several different wireless rain sensors on the market. My first target was an Acu-Rite 00875W rain gauge. I bought it two years ago and I don’t know if it’s still available now. This sensor turns out to be a huge pain. The main problem is that I can’t even register a consistent reading at 0 — every time I pop in the battery, I get a different signal that seems to have nothing to do with the previous readings. Also, the 0/1 bit patterns are completely unclear from the captured waveform — there are at least 4 or 5 different wavelengths. Here are two examples of the captured waveforms. They look nothing alike, even though both were captured right after the batteries are popped in and no rain has been detected.

After pulling my hair for a couple of days and finding no clue at all, I decided to give it up and try a different model. This time I bought an Acu-Rite 00899 wireless rain gauge. It’s probably worth explaining at first how the rain gauge works, because it’s quite a clever design. The outside of the transmitter unit looks like a bucket. Underneath the bucket is a plastic seesaw which swings left and right. Basically the rain water drains through the bucket hole onto the seesaw, and creates some motion to be detected.

At the bottom of the assembly is the battery compartment. Remove some tiny screws, the transmitter circuit is finally revealed. At the center is a reed switch, which is normally open but will close if there is a magnet nearby. It is very sensitive to magnetism. So where is the magnet? It’s on the bottom of the seesaw. The way this works is quite neat: the seesaw swings left and right, every time the magnet passes by the reed switch, it triggers a click. By detecting how many clicks there are within a given time, we know how heavy the rain is. Clever!

So let’s see if this rain gauge is easier to tackle. Following the same procedure as before, pop in the battery, power on the RF sniffing circuit, and launch the Audacity recording software, I got a waveform like the one shown in the image below.

Cool, this looks a lot better. I also made sure every time I pop in the battery I get the same waveform. So what patterns do I see here?

Each transmission consists of 3 repetitions of the same signal.
Every two repetitions are separated by a sync signal defined as 4 squarewaves of roughly 1.2ms wavelength.
The bit patterns are: logic 1 is defined by a constant high of 400us followed by a constant low of 200us; and logic 0 is defined by a constant high of 225us followed by a constant low of 400us.

The sync signal is actually very similar to the humidity/temperature sensor I described in the Part 2. The difference is that there is no 2.25ms constant low preceding the 4 squarewaves.

Given the timing data, here is the Arduino program to convert this signal into bits:

Download the Arduino Program for Sniffing Bits (rain gauge version)

Collect and Analyze Data. The transmitter sends a signal every two minutes, so it’s quite annoying that I had to wait two minutes for every reading. To create variations in data, I simply move the seesaw manually. This way I can precisely control how many clicks occurred between two readings. Here is a list of readings I captured. The numbers in the parentheses are the number of clicks since last reading, and the total number of clicks since the program started.

01110010 11111000 11110000 00000000 00000000 00000000 00000000 01011010 (0 / 0 total) 01110010 11111000 11110000 00000000 00000000 00000000 10000001 11011011 (1 / 1 total) 01110010 11111000 11110000 00000000 00000000 00000000 10000010 11011100 (1 / 2 total) 01110010 11111000 11110000 00000000 00000000 00000000 00000011 01011101 (1 / 3 total) 01110010 11111000 11110000 00000000 00000000 00000000 10000100 11011110 (1 / 4 total) 01110010 11111000 11110000 00000000 00000000 00000000 10000111 11100001 (3 / 7 total) 01110010 11111000 11110000 00000000 00000000 00000000 10001101 11100111 (6 / 13 total)
The encoding scheme is quite obvious: the first three bytes are the signature / device ID; the next 4 bytes record the total number of clicks since the transmitter is powered on. The leading bit of each byte is a parity bit (thanks to the lesson I learned from Part 2!) The last byte is for error checking.

This time I looked at the error checking byte more carefully, and noticed some interesting patterns. For example, everything else being the same, the change in its first bit matches the change of the first bit in the second to last byte. This suggest that perhaps the last byte is a parity byte — specifically, bit 0 is the parity of the first bits in all the preceding 7 bytes, and bit 1 is the parity of the second bit in all the preceding 7 bytes and so on. Just eyeballing the numbers, I believe this looks correct.

I felt quite happy that I made the right choice to abandon the first rain gauge which proved to be too difficult to solve. Well, dodging the challenge is not generally recommended, but in this particular case, I have no regret 🙂

Arduino Program and Validation. Here is the Arduino program that listens to the rain gauge and displays the number of clicks onto the serial monitor. The numbers have been validated with the display unit.